Wax paper sheet and coating therefor



'50 resistant.

Ltd llsm lton, No Drawing to Appl'eford Paper Ontario, CanadaApplication July 11, 1938, Serial No. 218,636

s PATENT OFFICE wi fwsxrsrnasnaarsgncosrma Seance, Ontario,

Products,-

10mm. an. 91-88) .This' invention relates to improvements in' waxedpaper sheets. -More particularly it relates to improvements in waxcoatings for paper sheets or the like and to the preparation of suchcoatings for application ,to sheets. Specifically, it relates to theprovision of a transparent mois-' ture proof heat sealable sheet ofpaper or the like which is suitableas a wrapping sheet wherever such asheet is desired for use.

I Heretofore heat scalable sheets have either been the low cost, lowtransparency wax paper sheets or the more expensive coated syntheticfilms. The latter type required in general that the coating be applieddissolvedin suitable solvents, which solvents had to be evaporated off.

Coatings of this latter type required expensive machinery not alwayspossessed by the paper products manufacturer who specialized in hot meltcoatings. v

The low cost waxed sheets which are in widespread use are low in cost tomanufacture as paraflln wax is commonly used as the coating material andas such coating can be applied as ahot melt by drawing a, sheet to becoated 25 through a vat containing the liquid coating but the sheets arelow in transparency. To increase the transparency one common practice isto mix a low melt point ester gum with the paramn. The ester gumincreases the transparency but reduces 30 the flexibility. While suchester gum paraflin coating can be applied" as a hot melt in the samemanner that paramn is applied and increasessubstantially thetransparency of the sheet it adds brittleness and the sheet does notheat seal as satisfactorily.

' Such coatings have heretofore been applied to thin tissue sheets ofvdifferent kinds. Unfllled sulphite sheets and glassine paper sheets havebeen widely used. Glassine is more transparent 40 and is greaseresistant as compared with the im- -nlled sulphite sheet but the coatingwhether. paraflin'alo'ne or the ester gum parailln combination hasa'tendency peel off the glassine' 4s Furthermore, such a coated sheetdoes not possess the desired pliability but possesses rather anundesirable brittleness when folded or creased, which disadvantage isparticularly unsatisfactory in a sheet designed to bemoisture Myimproved coated sheet possesses a high standard of pliability.- Thecoating does not tend to break or crack upon folding or creasingthesheet. Where the base sheet is ofsub- 55 stantia'l transparency theresulting transparency of the coated sheetis' particularly high. Myimprovedcoatedsheet-possessesahighglossand sealable ampoint ester proof,if a grease proof base sheet, such as glassine, is employed. My improvedcoating ad- ,heres securely to glassine and possesses high coh'esive aswell as adhesive characteristics. It is low in cost and thecoating maybe applied cheap- ,ly according to the hot melt method.

. I have discovered that if a substance of a rubbery consistency, moreparticularly hereinafter described, is added in a small quantity of from27 to 5% of the total mixture to amix of 10 ester gum and paraifln that,the coating will heat seal readily and form a particularly secure sealat the low temperatures of from 150 to 250 F.,

at whichsuchsealing is commercially carried on and that such results maybe obtained, even though the percentage of ester gum the mix isincreased substantially above that of, the paramp wax. Theresultingcoated sheet possesses all the desirable characteristics aboveenumerated and is particularly characterized by a high degree offlexibility without any tendency to break or crack along the line offold or crease.

My coating comprises:

Per cent Ester gum' i 50 to-90 g5 Wax (parailln) ..l 48 to 5 Substanceof rubbery consistencyl 2 to 5 A formulawhich I have found verysatisfactory is:

' Y Parts Ester gum approximately u 80 Wax approximately 20 Rubberapproximately 2to3 As the ester constitutes the bulk of the mixturecomposition the melting point of such gum determines the temperature at"which the I coating may be applied asa hot melt. It is desirabl'e thatsuch temperature be maintained low because it is desirable .to work atlow temperatures and it is not desirable to bring the paraillnwax,-which is'thewax commonly used, to a high temperature or to maintain itat such hightemperature for a protracted period because of the odorwhich it develops and which under certain conditions become permanent.Furthermore, the low melt point ester gums are more highly transparentthan the high melt gums, but the melting pointshould be sufllcientlyhigh so that the'coating will not be tacky at room temperatures. 1therefore prefer to employ a mixture of'highand low melt point ester.gums in the solution. A fifty-fifty mixture has been found suitable.Such a mixture possesses a high-degree of transparency and .is nottackyat-room' temperatures. 7

The ester gum increases the transparency of the coating substantiallyover that of a coating of paraiiin wax alone. The ester gum, however,

is notsatisfactory for use alone as a'coating because the coatingproduced by his so brittle that it would break and 'fiake ofi upon thebending of the sheet. Moreover, a sheet coated with ester gum alone oreven a combination of ester gum and paraflin will not heat sealsatisfactorily, providing the ester gum is present in the coatingmixture in such a proportion as to substantially increase thetransparency, and to provide the desired transparency it is necessary touse ester gum in the mixture in proportion of not less than 50% andpreferably to an extent of approximately The wax commonly used isparaflin wax and there is a variety of suitable melting point paraffins.Suitable animal, vegetable, or synthetic waxes might be used but theirprice and the fact that they frequently develop rancid odors aredeterents to their employment in general. Paraffin waxes within the A.S. T. M. melting range of to F. are satisfactory. A paraflin wax withinthe 133 to 136 F. range has been found highly satisfactory. Thisparafiin wax may constitute 5% to 50% of themixture. It is notordinarily desirable to increase the amount of paraffin over 50% as thetransparency of the coating is thereby materially reduced. A coatingconing to peel oiil When the rubbery substance is added however the heatseal is satisfactory and the coating is anchored securely to the basesheet. Where the word transparent is used herein to describe the .basesheet or the coated sheet it is not meant that the sheet is 100%transparent but that a commercial degree of transparency is attained. Itwould characterize, for example, a

sheet which might be termed semi-transparent or partially transparent.

Where the word Wax is used herein to describe this particularconstituent of the composition paraffin wax is meant or some othersuitable' wax such as herein set forth.

The substance of a rubber consistency need be added in only a smallpercentage of from 2% to 5%. Such percentage may however be increasedthough the amounts specified have been found suflicient and it is notdesirable to add such an amount of rubber as to increase the viscosityof i the molten coating too high. On the other hand, the rubberysubstance may be reduced in amount below 2 parts for 100 parts'of'mix.Even one per cent or less of rubber in the mixture is, helpful. Thisrubbery substance may be'in the form of crepe rubber or smoked rubbersheets- Synthetic rubber or a substance of a similar rubbery consistencywhich might not even be termed a true synthetic rubber may be used. Anexample of a synthetic material of a rubbery consistency which I havefound suitable is the polymer of iso-butylene (2 methyl propylene) soldunder the trade name of Vistanex-Medium.

This substance of a rubbery consistency must possess the capacity to gointo solution with'the.

' authorities might, however, term it a dispersion so finely divided anddistributed asnot to be visible. At least it is-a solution to *theextent thatv it does" not separate out and appears to be in solution.

In the preparation of my coating coin-position or mixture I mayincorporate as by means of a rubber mill or otherwise one part of thesubstance of a rubberyconslstency from with one to five parts of wax oralternative ester gum. I have found that two parts of wax worked in withone part of the substance of a rubbery consistency is ,verysatisfactory. This mixture of the rubbery substance and wax is thenmelted together with the necessary wax and ester gum to complete theformula. This operation may be conveniently carried out in the actualtanks of the coating machine. The melt is stirred until homogeneous andthe rubbery substance goes into solution as described. When the termsubstance of a rubbery consistency or rubbery substance is used hereinit is intended to include synthetic sub-' stances such as above setiorthas well asthe have found preferable is to gradually add small fragmentsof pale crepe rubber sheets to a solution of molten paraflln heated toapproximately 20 0. 'above its melt point while subjecting said-solutionduring such incorporation to violent stirring and agitation. Suchtemperature and j agitation should be continued for the time required tobring the rubbery substance completely into solution, which should beaccomplished within twelve hours or less. The ester gum constituents maythen be stirred into the solution and thoroughly incorporated therein.

The sheet material to be coated is then run through the machine in theordinary manner of application of a hot melt coating. In one preferredform of the. invention the base sheet is a plasticized glassine. A finetissue sheet, such as an unfilled sulphite sheet, may be used whichwould produce, a strong sheet though less transparent than the coatedglassine sheet. The resulting coated sheet possesses high transparency.For example, if glassin'eis employed the coated sheet possesses asubstantially higher degree .of transparency than the base. glassinesheet. The coated sheet hot seals splendidly, ls non-tacky,

possesses a fine gloss, and is substantially trans-.

